It is known to utilise laser light for tissue treatment, such as cosmetic tissue resurfacing, removal of hair, photocoagulation of veins, etc.
During cosmetic tissue resurfacing, a laser ablates a thin epidermal layer of illuminated derma of a patient. During healing, a new epidermal layer is formed on the ablated surface having the look of the derma of a young person, i.e. the new epidermal layer is formed without previously existing scars, wrinkles, etc.
Lasers that operate at a wavelength that is absorbed in water are used for cosmetic tissue resurfacing. When the laser power density (W/mm.sup.2) at illuminated cells is sufficient, cellular water is superheated causing small explosions that disrupt heated cells.
During removal of an epidermal layer, it is essential not to damage underlying or surrounding tissue. Residual heat may cause non-ablated cells to char and become necrotic, whereby new scars may be formed and thus, it is desirable to apply laser power for a short time, to minimize transmission of conducted heat to underlying and surrounding tissue.
It is therefore desired to accurately control the amount of light energy transferred to derma to be ablated. The amount of energy must be sufficient for the dermal cells to vaporize and, simultaneously, the amount of residual energy heating non-ablated cells must be so low that non-ablated cells will not be damaged.
Apparatuses for cosmetic tissue resurfacing are known, comprising a CO.sub.2 laser emitting a laser beam and a laser articulating arm with mirrors for reflection of the laser beam, so that the laser beam is transmitted inside the articulating arm. Further, the arm has a number of joints, so that the arm can be moved around by an operator. A handpiece to be held by the operator is connected to the arm. The laser beam is moved or scanned across a target surface by movable mirrors connected to motors and mounted in the arm. The scan pattern of the laser beam is an archimedes spiral. The laser spot formed by the laser beam on the target surface moves along the spiral at a constant angular speed.
It is a disadvantage of the known apparatus that the energy density delivered to the target surface is non-uniform across the scanned surface area of the spiral, as more energy is delivered at the centre of the spiral than at the circumferential of the spiral.
It is another disadvantage of the known apparatus that the circular outline of the scan pattern leads to non-uniform scanning of an area that is larger than the area of the scan spiral as either 1) areas that have not been scanned will remain on the surface, when abutting spirals or 2) ablated areas will be scanned more than once, due to overlap of spirals.
It is yet another disadvantage of the known apparatus that evaporated derma is exhausted through the internal of the laser articulation arm, whereby optics and other members in the arm get dirty.
It is still another disadvantage of the known apparatus that it is very laborious to disassemble members, that may have been in contact with a patient, from the handpiece, e.g., for autoclaving.
It is still another disadvantage of the known apparatus that movement of the handpiece is restrained by the laser articulation arm, as the construction of tubes interconnected by joints is not fully flexible.
In addition, the apparatus typically has a large mass and a large inertia (typically also due to counter-balancing masses) which makes the operation and movement of the arm elaborate and heavy.
Under the name Uni-laser 450P, Asah Medico A/S, Denmark, markets an apparatus for cosmetic tissue resurfacing, comprising a CO.sub.2 laser and an optical fiber coupled to the laser at one end and to a handpiece at the other end. The laser beam is manually scanned across the treatment surface by corresponding movement of the handpiece whereby the quality of the treatment is determined and limited by the skill of the operator.
Apart from being able to accurately control the amount of light energy transmitted towards tissue to be treated, it is also desirable to be able to automatically control whether or not light is transmitted towards tissue. If, for example, a laser is pointed at healthy tissue, it is desirable that it is detected that the tissue is healthy and that transmission of a laser beam be inhibited whereby damage to healthy tissue is prevented.
It is a disadvantage of known apparatuses that the exact circumference of the surface tissue area to be treated is defined manually by the operator. Manual control easily results in accidental damage to healthy tissue due to involuntary movements of the hand.
In U.S. Pat. No. 5,531,740, an apparatus is disclosed for automatically delivering a laser beam to an intricated colored region of a treatment area, e.g. for laser photocoagulation treatment of malformed veins. Typically, venular malformation forms an extremely intricate pattern and consequently, the task of precisely delivering the laser beam exclusively to the malformed veins becomes quite formidable. During scanning over the treatment region, the color of tissue to be treated is detected and the laser automatically treats only areas having a specified color.
It is a disadvantage of the apparatus that it is bulky and cannot easily be moved into treatment positions in relation to various surfaces of a human body. Rather, a tissue surface to be treated has to be brought into a specific position in relation to the apparatus before treatment can take place.
It is still another disadvantage of the known apparatuses that the distance between the surface to be treated and the output laser beam optics is unknown so that the degree of focusing of the laser beam on the surface to be treated is dependent on the operator.
It is yet another disadvantage of known apparatuses that no feed-back on the quality of the treatment currently in progress is provided.